Heretofore, there has been reflected light detecting apparatus that irradiates illumination onto an object, and detects reflected light therefrom. As a way of making practical use of this reflected light detecting apparatus, there is detection sensor that detects a person or an object.
For example, as shown in FIG. 25, in an automatic door system 100, an illumination irradiating apparatus 111 of a reflected light detecting apparatus 100 projects light onto a position through which a person as being a verification object (detection object) 101 passes, and a light receiving element 112 detects reflected light of the projected light. When detecting reflection, the reflected light detecting apparatus 110 determines that a man is passing therethrough, and opens a door 102.
Incidentally, the light irradiated from the illumination irradiating apparatus 111 of the reflected light detecting apparatus 110 may be infrared-rays other than spot light such as illumination, laser beam and the like.
As another use of the reflected light detecting apparatus, the reflected light detecting apparatus may be used as discriminating apparatus that discriminates a detection object on the basis of whether the reflected light is detected or not. For example, the reflected light detecting apparatus is used to discriminate a flat-shaped object such as a sheet of paper, a metal plate or the like according to whether it has gloss or not.
As techniques relating to the reflected light detecting apparatus, there has been a technique (refer to Patent Document 1, below) in which a plurality of reflective sensors are arranged to detect not only presence/absence of a detection object but also a traveling direction of the detection object by using a time lag of the detection time, and a technique (refer to Patent Document 2, below) in which a plurality of light emitting elements is arranged, and irradiates light onto a detection object to measure a surface shape of the detection object by detecting the reflected light by a photosensitive element.
In the technique taught in Patent Document 2 below, the plural light emitting elements are used to drive a plurality of distance sensors in order to measure the surface shape of the detection object.
Meanwhile, the reflected light detecting apparatus that irradiates illumination onto a detection object and detects reflection of the illumination has a disadvantage that the reflected light detecting apparatus is easily affected by disturbance light. In other words, in environments where disturbance light such as sunlight, external illumination or the like exists, the reflected light detecting apparatus could accidentally mistake external light (disturbance light) other than light irradiated from the reflected light detecting apparatus itself for reflected light from an object onto which the reflected light detecting apparatus irradiated the light.
In concrete, as shown in FIG. 26(a), for example, in an image 121a where a verification object 120 irradiated illumination thereon is photographed, reflected light beams 122 and 123 of irradiated illumination appears on the verification object 120 in the image 121a under situation where the surface of the verification object 120 reflects light and no disturbance light exists.
To the contrary, as shown in FIG. 26(b), under situation where disturbance light exists, disturbance light beams 124a-124c and a light beam 125, which is disturbance light entering onto the verification object 120, are photographed, along with the reflected light beams 122 and 123.
Under situation where disturbance light exists as above, the reflected light detecting apparatus could accidentally mistake the disturbance light 124a to 124c and 125 for the reflected light beams 122 and 123.
Furthermore, as shown in FIG. 27(a), in an image 131a where a verification object 130 irradiated illumination thereon is photographed, no light is in the image 131a under situation where the surface of the verification object 130 does not reflect light and no disturbance light exists.
To the contrary, as shown in FIG. 27(b), disturbance light beams 132a, 132b, 133a and 133b enter in the image 131b under situation where disturbance light exists.
In the above case, the reflected light detecting apparatus could accidentally mistake disturbance light beams 132a, 132b, 133a and 133b, particularly, the disturbance light beams 133a and 113b entering onto the verification object 130 in the image 131b, for reflected light beams. Incidentally, when the reflected light detecting apparatus is applied as the above discriminating apparatus, the apparatus could accidentally mistake the disturbance light beams 133a and 133b for reflected light beams, and erroneously conclude that the verification object 130 is one that reflects light.
One of the possible measures is that a light source of disturbance light is specified and the light source is turned off or arrangement of the reflected light detecting apparatus is changed to prevent light irradiated from the light source from entering into the image. However, as the disturbance light, there can be sunlight entering from the window, surrounding illumination, etc. It is difficult to specify light sources of these kinds of disturbance light, and more difficult to specify a light source to prevent the disturbance light from entering into the image. Particularly, when the disturbance light is caused from sunlight, erroneous detection due to the disturbance could occur light in only a specific time zone because the illuminating angle or the like of the sun changes according to the season or time. Accordingly, reproducibility of erroneous detection due to disturbance light is largely lowered much, which causes an increase in time to specify the disturbance light, for example.
Therefore, there is a technique that employs a data-like pulse beam as the light beam to be irradiated onto the verification object, and determines that the verification object is detected (that is, the reflected light is detected) when a photo detector receives a designated data-like pulse beam (refer to Patent Document 3 below, for example).
Patent Document 1: Japanese Patent Laid-Open Publication No. 2000-075046
Patent Document 2: Japanese Patent Laid-Open Publication No. H08-178632
Patent Document 3: Japanese Patent Laid-Open Publication No. 2002-148352